Until now, glass has been generally used as a composition material of an optical element (mainly lens) from the viewpoint that glass has excellent optical characteristics and mechanical hardness. Miniaturization of an optical element has been required with the advance of miniaturization of an apparatus in which an optical element is used. It is difficult to produce a glass lens having an aspheric form or a complicated form, and glass is becoming an unsuitable material in respect of a mass production of a precise optical element. As a result, a plastic material which can be easily processed has been increasingly examined and used for an optical element. Examples of such plastic material are thermoplastic resins having an excellent transparency (light transmittance), such as polyolefin and polycarbonate.
In recent years, in addition to an optical pickup apparatus used for a CD recording material using a conventional light source emitting a light of about 780 nm, and an optical pickup apparatus used for a DVD recording material using a light source emitting a light of about 650 nm, there has been developed an optical apparatus incorporating an optical pickup apparatus used for a recording material like as Blu-ray disc which is increased a recording density by using a light of a short wavelength from blue to blue-violet in the range of 350 nm to 450 nm and by increasing a number of aperture (NA) of an optical system. When an optical element made of a plastic is used for an optical apparatus having a high NA and using a light source emitting a light of a short wavelength, there have been raised problems of deformation and transformation of an optical element. These problems were caused by strongly focused laser flux as well as a laser having a higher energy than a conventional laser, resulting in an increased stress to the interface of an optical element, and as a result, the materials composing the optical element become unstable. These deformation and transformation are very minute scale and they will not be a level to cause problems in a conventional optical apparatus. However, it was found that in an optical apparatus of high density, they will cause problems to affect the performance of the optical apparatus. In order to solve these problems, it was proposed an optical element made of a polyolefin resin having an alicyclic structure, which has a relatively high transmittance to a blue light and has as high light-fastness (for example, refer to Patent Document 1). However, in order to use as an optical element used for this kind of optical apparatus, there is required to provide an anti-reflection layer so as to prevent a loss of light and a apparition of light diffusion due to a light reflection at a surface of an optical element, even if the light transmittance of a resin material is increased. Consequently, a stress is concentrated at an interface between an anti-reflection layer and a resin, and this will promote to occur the problems as described above. Therefore, further improvement is required.
Patent Document 1: Japanese patent application open to public inspection (JP-A) No. 2003-73559.